Electronic locks have a number of advantages over normal mechanical locks. They may be encrypted so that only a key carrying the correct code will operate the lock, and they may also contain normal mechanical tumblers. They may contain a microprocessor so that, for example, a record can be kept of who has operated the lock in a certain time period, or so that they are only operable at certain times. They may also have the advantage that, if a key is lost the lock may be reprogrammed to prevent the risk of a security breach, or to avoid the expense of replacement.
Locks utilising some type of electronic element are known.
U.S. Pat. No. 5,542,274 discloses a lock having a key-operated, rotatable cylinder. A latching element is located in the region of the boundary surface between the cylinder housing and the cylinder and is resiliently urged by springs into a groove in the cylinder. An electrically actuable blocking element is moveable between a release position in which the latching element can be moved out of the recess when the cylinder is rotated, and a blocking position. The cylinder cannot be turned by means of the key when the blocking element is in its blocking position because the blocking element prevents the latching element from being moved out of the groove in the cylinder.
U.S. Pat. No. 5,552,777 discloses a mechanical lock and key including an electronic access control feature for preventing opening of the lock, even with the correct mechanical key unless prescribed conditions are met. A cylinder rotatable in a cylinder housing is fitted with an “ID chip” and a switch connected to a solenoid capable of withdrawing a blocking pin when energised. The blocking pin is resiliently urged by a spring into a bore in the cylinder housing when the cylinder is in the locked position. When a key, containing a battery, microprocessor and database, is inserted into the lock an electrical connection is made to the ID chip, if the serial number of the ID chip matches one of the numbers held in the database, the key is authorised to open the lock. The switch is activated and the solenoid energised withdrawing the blocking pin against the action of the spring enabling mechanical opening of the lock.
WO 01/55539 discloses an electronic locking system having a cylinder housing in which a cylinder is rotatable, and having a lock member moveable between a locked position and an open position under the influence of a solenoid. In the locked position, the lock member prevents a spring loaded locking pin in the cylinder from being moved out of engagement with a cavity in the cylinder housing and so interferes with the rotary movement of the cylinder. The solenoid is energised when a key containing a power source and generating the correct signal is inserted into the lock, so moving the locking member into its open position and allowing the cylinder to be rotated.
All of the above locks suffer from the disadvantages that they are relatively complex and cumbersome and that they require mechanical springs to return the locking element to its locked position once the current has been removed. This leads to an increase in the space required within the lock for the locking members, and can also lead to a reduced life span of the lock caused by mechanical failure of the springs.
The lock cylinder assembly of the present invention seeks to obviate or mitigate the above disadvantages by providing a locking member that can be moved both into and out of its locked position without the need for any mechanical springs or other mechanical biasing means.